Facing a potential Republican surge at November's midterm elections, Democratic candidates are clamoring for Hillary Clinton to join them on the campaign trail.

The former secretary of state's high ratings and connections to a vast roster of major party contributors makes her the most sought after surrogate for Democratic hopefuls in a difficult election year.

In contrast, President Barack Obama is expected to have a muted role due to his dropping popularity.

While Clinton undoubtedly wants to see her party do well on November 4, a return to town halls and diners will give her a chance to test speech themes and flex her retail politics muscles ahead of her own likely run for president in 2016.

Clinton's last campaign was in 2008 and she has looked rusty as she promotes her memoir "Hard Choices," stumbling over media questions about her personal wealth and lucrative speeches.

Helping fellow Democrats will also bolster her existing network of party allies throughout the country should she chose to make a White House bid.

But the former senator will have to pick her appearances and endorsements carefully to avoid association with too many losing candidates in the fall, when Republicans are tipped by pundits to keep the House of Representatives and perhaps gain the six seats they need to take control of the Senate.

"I've heard from virtually every incumbent and candidate that she is at the top of their list," said New York congressman Steve Israel, chairman of the Democratic Congressional Campaign Committee.

That makes her more popular with House Democratic campaigns than former President Bill Clinton, a veteran campaigner, although her husband's approval ratings with the public are higher than hers.

Israel said Hillary Clinton had indicated to him her willingness to get involved in the midterms, when traditionally the president's party is more likely to struggle.

"Hillary and Bill Clinton can go into any battleground district in the United States and be an asset," Israel said. "She helps turn out our base, she helps with independent voters, she helps with fundraisers."

Both the DCCC and the Democratic Senatorial Campaign Committee are using Clinton's book as a fundraising tool in emails to supporters.

They ask voters to submit their name for a chance to win a copy of the book, thus building a list of her supporters who can be contacted to turn out at the midterm election campaign.

"Ready For Hillary" - a well-funded group that supports a Clinton 2016 candidacy by identifying and organizing millions of voters around the country - altered its federal registration in May so it can be a vessel for funding midterms campaigns.

The group has contributed to state Democratic parties by sponsoring dinner and convention sponsorships in states like New Hampshire, which is both home to a contested Senate race in November and an influential early-voting state that Clinton would aim to win in a presidential race.

Voters are slightly more likely to support a congressional candidate backed by Clinton than by Obama, according to a March poll by the Wall Street Journal and NBC News.

A quarter of voters said a Hillary Clinton endorsement could sway them, compared to 22 percent for Obama. A separate Wall Street Journal/NBC News poll showed 44 percent of voters view Clinton positively and 37 percent see her negatively.

Seventy percent of Republicans and a chunky 40 percent of independents said in that poll there was no chance they would vote for Clinton in 2016, suggesting her main role in the midterms could be to energize Democrats and raise funds rather than win over undecided voters.

READY FOR KENTUCKY?

Kentucky Democrat Alison Lundergan Grimes is a prime example of a candidate keen to benefit from Clinton's heft.

"Alison thinks of Secretary Clinton as a mentor and has spoken with her multiple times throughout the campaign," said a campaign aide for Grimes.

In a tough fight to win a U.S. Senate seat from Minority Leader Mitch McConnell, Grimes has distanced herself from Obama, whose tightening of regulation of power plants is deeply unpopular in the coal-producing state.

Though criticized by Republicans for spearheading what they call Obama's feckless foreign policy, Clinton is more distant from the president's domestic agenda like his energy policy.

"President Obama's poll numbers are terrible (and) Democrats have someone who does not have that same sort of popularity challenge, but is still connected enough, and still seen as a very prominent national figure.

"Essentially, she is presidential without all the baggage the president has," said John Hudak, an expert on presidential campaigns with the Brookings Institution.

But any run for the presidency could suffer if she backs candidates that go on to lose, said Democratic strategist Hank Sheinkopf, who worked on Bill Clinton's 1996 re-election campaign.

"If there are failures she can be blamed for them. The Hillary campaign team's challenge is choosing seats that she can win," he said.

Clinton made Democrats nervous in May by saying in a Washington speech she would "leave (the midterm) discussion to others," which was taken to mean she would not spend much time helping Democrats.

Further questions about her involvement arose after the only candidate she has raised money for - one-time representative Marjorie Margolies, the mother-in-law of Clinton's daughter Chelsea - lost her Pennsylvania primary vote.

But Clinton is widely expected to wade in after she finishes the national publicity tour for her book late in the summer.

"She has always worked hard to advance Democratic candidates and will do so again when the time is right," Clinton spokesman Nick Merrill said.

Clinton has looked most vulnerable when discussing her personal wealth and when Republicans pick at her foreign policy record on Iraq, Russia and the 2012 attack on the US diplomatic compound in Benghazi, Libya.

She was criticized as out of touch for suggesting in an interview with The Guardian newspaper at the weekend that she was not "truly well off."

The last time Clinton and her husband released tax returns, in 2007, they showed the Clintons had earned $109 million jointly since 2000. She has been giving a series of speeches that earn her up to $250,000 each since leaving the State Department in 2013.